Study Assesses Needle Heat

WARREN, Mich. — Industrial sewing is one of the most common manufacturing operations in the automotive industry, producing an array of products such as dashboard padding, air bags, seat cushions and backs from synthetic fabric, plastic and leather. During the high-speed process -- which often exceeds 2000 stitches per minute -- friction between the needle and the fabric causes the needle to heat, creating potential for thread breakage and fabric damage. Manufacturers would like to improve efficiency by increasing sewing speed, but heat buildup remains an obstacle.

The operation of the sewing machine is a deceptively complex process. The needle temperature rises until steady state is reached and then oscillates with each stitch throughout the process. Complex heat flow transients also occur between the needle and the thread, and between the needle and the fabric. Motion of the needle through the fabric both generates and dissipates heat, so pauses in operation and changes in sewing direction often generate sudden temperature peaks.

In a joint study conducted by General Motors Corp., the University of Windsor in Ontario, Canada, and Delphi Interior and Lighting Systems in Troy, Mich., researchers used finite element analysis to characterize the performance of high-speed sewing machine needles in the automotive industry, and infrared radiometric imaging to confirm the validity of the models.

A high-speed IR thermogram of a sewing needle operating at 1000 rpm indicates areas of heat, which could lead to thread or fabric damage. Courtesy of General Motors Corp.
They used the Ansys Parametric Design Language to establish the finite element analysis model, which correlates the relationship among geometric parameters, material properties and operating conditions, and which presents a map of the heating results. They then used IR imaging radiometry to verify the model, running simulations for sewing speeds of 500, 1000 and 2000 rpm, and for fabric thicknesses of 2 and 4 mm. They compared the results of the thermal images obtained for each of these conditions under actual operating conditions, finding consistent correlation between the models and the experimental results.

The study revealed interesting information that can be used as a guide to optimize the process and increase product yield, according to Daniel L. Simon of General Motors' Center of Expertise in Infrared Technology. "Suggestions to machine operators are already being implemented regarding the adjustments of sewing speed to avoid thread overheating when reaching corners and ending runs," he said. "Simple steps like these can go a long way toward boosting quality, improving yield and eliminating scrap."